One document matched: draft-ietf-httpbis-alt-svc-11.xml
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<!DOCTYPE rfc
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<rfc ipr="trust200902" category="std" docName="draft-ietf-httpbis-alt-svc-11">
<front>
<title>HTTP Alternative Services</title>
<author initials="M." surname="Nottingham" fullname="Mark Nottingham">
<organization>Akamai</organization>
<address>
<email>mnot@mnot.net</email>
<uri>https://www.mnot.net/</uri>
</address>
</author>
<author initials="P." surname="McManus" fullname="Patrick McManus">
<organization>Mozilla</organization>
<address>
<email>mcmanus@ducksong.com</email>
<uri>https://mozillians.org/u/pmcmanus/</uri>
</address>
</author>
<author initials="J. F." surname="Reschke" fullname="Julian F. Reschke">
<organization abbrev="greenbytes">greenbytes GmbH</organization>
<address>
<email>julian.reschke@greenbytes.de</email>
<uri>https://greenbytes.de/tech/webdav/</uri>
</address>
</author>
<date year="2016" month="February" day="3"/>
<area>Applications and Real-Time</area>
<workgroup>HTTP Working Group</workgroup>
<keyword>HTTP</keyword>
<keyword>ALPN</keyword>
<keyword>Alternative Services</keyword>
<abstract>
<t>
This document specifies "Alternative Services" for HTTP, which allow an
origin's resources to be authoritatively available at a separate network
location, possibly accessed with a different protocol configuration.</t>
</abstract>
<note title="Editorial Note (To be removed by RFC Editor)">
<t>
Discussion of this draft takes place on the HTTPBIS working group mailing list
(ietf-http-wg@w3.org), which is archived at <eref target="https://lists.w3.org/Archives/Public/ietf-http-wg/"/>.
</t>
<t>
Working Group information can be found at <eref target="http://httpwg.github.io/"/>; source code and issues
list for this draft can be found at
<eref target="https://github.com/httpwg/http-extensions"/>.
</t>
<t>
The changes in this draft are summarized in <xref target="change.log"/>.
</t>
</note>
</front>
<middle>
<section anchor="introduction" title="Introduction">
<t>
HTTP <xref target="RFC7230"/> conflates the identification of
resources with their location. In other words, "http://" (and "https://") URIs are
used to both name and find things to interact with.
</t>
<t>
In some cases, it is desirable to separate identification and location in HTTP; keeping the same
identifier for a resource, but interacting with it at a different location on the network.
</t>
<t>For example:
<list style="symbols">
<t>
An origin server might wish to redirect a client to a different server
when it is under load, or it has found a server in a location that is
more local to the client.
</t>
<t>
An origin server might wish to offer access to its resources using a new
protocol (such as HTTP/2, see <xref target="RFC7540"/>) or one using improved
security (such as Transport Layer Security (TLS), see <xref target="RFC5246"/>).
</t>
<t>
An origin server might wish to segment its clients into groups of
capabilities, such as those supporting Server Name Indication (SNI,
see Section 3 of <xref target="RFC6066"/>) and those not
supporting it, for operational purposes.
</t>
</list>
</t>
<t>
This specification defines a new concept in HTTP, "Alternative Services",
that allows an origin server to nominate additional means of interacting with it on
the network. It defines a general framework for this in <xref target="alternative"/>, along with specific mechanisms for advertising their
existence using HTTP header fields (<xref target="alt-svc"/>) or HTTP/2
frames (<xref target="frame"/>), plus a way to indicate that an alternative
service was used (<xref target="indicator"/>).
</t>
<t>
It also endorses the status code 421 (Misdirected Request) (<xref target="status"/>)
that origin servers (or their nominated alternatives) can use to indicate that they
are not authoritative for a given origin, in cases where the wrong location is used.
</t>
<section anchor="notational-conventions" title="Notational Conventions">
<t>
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD",
"SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be
interpreted as described in <xref target="RFC2119"/>.
</t>
<t anchor="imported.abnf">
This document uses the Augmented BNF defined in <xref target="RFC5234"/> and
updated by <xref target="RFC7405"/>
along with the "#rule" extension defined in Section 7 of <xref target="RFC7230"/>.
The rules below are defined in <xref target="RFC5234"/>, <xref target="RFC7230"/>, and <xref target="RFC7234"/>:
</t>
<figure><artwork type="abnf2616"><![CDATA[
OWS = <OWS, see [RFC7230], Section 3.2.3>
delta-seconds = <delta-seconds; see [RFC7234], Section 1.2.1>
port = <port, see [RFC7230], Section 2.7>
quoted-string = <quoted-string, see [RFC7230], Section 3.2.6>
token = <token, see [RFC7230], Section 3.2.6>
uri-host = <uri-host, see [RFC7230], Section 2.7>
]]></artwork></figure>
</section>
</section>
<section anchor="alternative" title="Alternative Services Concepts">
<t>
This specification defines a new concept in HTTP, the "Alternative Service".
When an origin (see <xref target="RFC6454"/>) has resources that are accessible through a
different protocol / host / port combination, it is said to have an alternative
service available.
</t>
<t>
An alternative service can be used to interact with the resources on an origin
server at a separate location on the network, possibly using a different
protocol configuration. Alternative services are considered authoritative for
an origin's resources, in the sense of <xref target="RFC7230"/>, Section 9.1.
</t>
<figure>
<preamble>For example, an origin:</preamble>
<artwork type="example"><![CDATA[
("http", "www.example.com", "80")
]]></artwork>
</figure>
<figure>
<preamble>might declare that its resources are also accessible at the alternative service:</preamble>
<artwork type="example"><![CDATA[
("h2", "new.example.com", "81")
]]></artwork>
</figure>
<t>
By their nature, alternative services are explicitly at the granularity of an
origin; i.e., they cannot be selectively applied to resources within an origin.
</t>
<t>
Alternative services do not replace or change the origin for any given resource;
in general, they are not visible to the software "above" the access mechanism.
The alternative service is essentially alternative routing information that can
also be used to reach the origin in the same way that DNS CNAME or SRV records
define routing information at the name resolution level. Each origin maps to a
set of these routes — the default route is derived from the origin itself and the
other routes are introduced based on alternative-service information.
</t>
<t>
Furthermore, it is important to note that the first member of an alternative
service tuple is different from the "scheme" component of an origin; it is more
specific, identifying not only the major version of the protocol being used,
but potentially communication options for that protocol.
</t>
<t>
This means that clients using an alternative service can change the host, port
and protocol that they are using to fetch resources, but these changes MUST NOT
be propagated to the application that is using HTTP; from that standpoint, the
URI being accessed and all information derived from it (scheme, host, port) are
the same as before.
</t>
<t>
Importantly, this includes its security context; in particular, when TLS
<xref target="RFC5246"/> is used to authenticate, the alternative service will need to present a certificate
for the origin's host name, not that of the alternative. Likewise, the Host
header field (<xref target="RFC7230"/>, Section 5.4) is
still derived from the origin, not the alternative service (just as it would
if a CNAME were being used).
</t>
<t>
The changes MAY, however, be made visible in debugging tools, consoles, etc.
</t>
<t>
Formally, an alternative service is identified by the combination of:
<list style="symbols">
<t>An Application Layer Protocol Negotiation (ALPN) protocol name, as per
<xref target="RFC7301"/></t>
<t>A host, as per <xref target="RFC3986"/>, Section 3.2.2</t>
<t>A port, as per <xref target="RFC3986"/>, Section 3.2.3</t>
</list>
</t>
<t>
The ALPN protocol name is used to identify the application protocol or
suite of protocols used by the alternative service. Note that for the
purpose of this specification, an ALPN protocol name implicitly
includes TLS in the suite of protocols it identifies, unless specified
otherwise in its definition. In particular, the ALPN name "http/1.1",
registered by Section 6 of <xref target="RFC7301"/>, identifies
HTTP/1.1 over TLS.
</t>
<t>
Additionally, each alternative service MUST have:
<list style="symbols">
<t>A freshness lifetime, expressed in seconds; see <xref target="caching"/></t>
</list>
</t>
<t>
There are many ways that a client could discover the alternative service(s)
associated with an origin. This document describes two such mechanisms:
the "Alt-Svc" HTTP header field (<xref target="alt-svc"/>) and the "ALTSVC" HTTP/2 frame type
(<xref target="frame"/>).
</t>
<t>
The remainder of this section describes requirements that are common to alternative
services, regardless of how they are discovered.
</t>
<section anchor="host_auth" title="Host Authentication">
<t>
Clients MUST NOT use alternative services with a host that is different from the origin's
without strong server authentication; this mitigates the attack described in
<xref target="host_security"/>. One way to achieve this is for the alternative to use TLS
with a certificate that is valid for that origin.
</t>
<t>
For example, if the origin's host is "www.example.com" and an alternative is
offered on "other.example.com" with the "h2" protocol, and the certificate
offered is valid for "www.example.com", the client can use the alternative.
However, if "other.example.com" is offered with the "h2c" protocol, the client
cannot use it, because there is no mechanism in that protocol to establish
strong server authentication.
</t>
</section>
<section anchor="caching" title="Alternative Service Caching">
<t>
Mechanisms for discovering alternative services also associate a freshness
lifetime with them; for example, the Alt-Svc header field uses the "ma"
parameter.
</t>
<t>
Clients can choose to use an alternative service instead of the origin at any
time when it is considered fresh; see <xref target="switching"/> for specific
recommendations.
</t>
<t>
Clients with existing connections to an alternative service do not need to
stop using it when its freshness lifetime ends; i.e., the caching
mechanism is intended for limiting how long an alternative service can be used
for establishing new connections, not limiting the use of existing ones.
</t>
<t>
Alternative services are fully authoritative for the origin in question, including
the ability to clear or update cached alternative service entries, extend freshness
lifetimes, and any other authority the origin server would have.
</t>
<t>
When alternative services are used to send a client to the most optimal server, a change in
network configuration can result in cached values becoming suboptimal. Therefore, clients SHOULD
remove from cache all alternative services that lack the "persist" flag with the value "1" when
they detect such a change (when information about network state is available).
</t>
</section>
<section anchor="requiring-server-name-indication" title="Requiring Server Name Indication">
<t>
A client MUST only use a TLS-based alternative service if the client also
supports TLS Server Name Indication (SNI). This supports the conservation of
IP addresses on the alternative service host.
</t>
<t>
Note that the SNI information provided in TLS by the client will be that of the origin, not the
alternative (as will the Host HTTP header field value).
</t>
</section>
<section anchor="switching" title="Using Alternative Services">
<t>
By their nature, alternative services are OPTIONAL: clients do not need to
use them. However, it is advantageous for clients to behave in a predictable
way when alternative services are used by servers (e.g., for load balancing).
</t>
<t>
Therefore, if a client becomes aware of an alternative service, the client
SHOULD use that alternative service for all requests to the associated origin
as soon as it is available, provided the alternative service information
is fresh (<xref target="caching"/>) and the security properties of the
alternative service protocol are desirable, as compared to the existing
connection. A viable alternative service is then treated in every way as the
origin; this includes the ability to advertise alternative services.
</t>
<t>
If a client becomes aware of multiple alternative services, it chooses
the most suitable according to its own criteria (again, keeping security
properties in mind). For example, an origin might advertise multiple
alternative services to notify clients of support for multiple versions of
HTTP.
</t>
<t>
A client configured to use a proxy for a given request SHOULD NOT
directly connect to an alternative service for this request, but instead route it
through that proxy.
</t>
<t>
When a client uses an alternative service for a request, it can indicate
this to the server using the Alt-Used header field (<xref target="indicator"/>).
</t>
<t>
The client does not need to block requests on any existing connection; it can be
used until the alternative connection is established. However, if the security
properties of the existing connection are weak (e.g. cleartext HTTP/1.1) then
it might make sense to block until the new connection is fully available in
order to avoid information leakage.
</t>
<t>
Furthermore, if the connection to the alternative service fails or is unresponsive, the client
MAY fall back to using the origin or another alternative service. Note, however, that this
could be the basis of a downgrade attack, thus losing any enhanced security properties of the
alternative service. If the connection to the alternative service does not negotiate the
expected protocol (for example, ALPN fails to negotiate h2, or an Upgrade request to h2c is
not accepted), the connection to the alternative service MUST be considered to have failed.
</t>
</section>
</section>
<section anchor="alt-svc" title="The Alt-Svc HTTP Header Field">
<t>
An HTTP(S) origin server can advertise the availability of alternative services
to clients by adding an Alt-Svc header field to responses.
</t>
<figure>
<artwork type="abnf2616"><![CDATA[
Alt-Svc = clear / 1#alt-value
clear = %s"clear"; "clear", case-sensitive
alt-value = alternative *( OWS ";" OWS parameter )
alternative = protocol-id "=" alt-authority
protocol-id = token ; percent-encoded ALPN protocol name
alt-authority = quoted-string ; containing [ uri-host ] ":" port
parameter = token "=" ( token / quoted-string )
]]></artwork>
</figure>
<t>
The field value consists either of a list of values, each of which indicates one
alternative service, or the keyword "clear".
</t>
<t>
A field value containing the special value "clear" indicates that the
origin requests all alternatives for that origin to be invalidated (including
those specified in the same response, in case of an invalid reply containing
both "clear" and alternative services).
</t>
<t>
ALPN protocol names are octet sequences with no
additional constraints on format.<!-- besides length?-->
Octets not allowed in tokens (<xref target="RFC7230"/>, Section 3.2.6)
MUST be percent-encoded as per Section 2.1 of <xref target="RFC3986"/>.
Consequently, the octet representing the percent character "%" (hex 25) MUST
be percent-encoded as well.
</t>
<t>
In order to have precisely one way to represent any ALPN protocol name, the following
additional constraints apply:
<list style="numbers">
<t>
Octets in the ALPN protocol name MUST NOT be percent-encoded if they are valid
token characters except "%", and
</t>
<t>
When using percent-encoding, uppercase hex digits MUST be used.
</t>
</list>
</t>
<t>
With these constraints, recipients can apply simple string comparison to
match protocol identifiers.
</t>
<t>
The "alt-authority" component consists of an OPTIONAL uri-host
("host" in Section 3.2.2 of <xref target="RFC3986"/>), a colon (":"),
and a port number.
</t>
<figure>
<preamble>For example:</preamble>
<artwork type="example"><![CDATA[
Alt-Svc: h2=":8000"
]]></artwork>
<postamble>
This indicates the "h2" protocol (<xref target="RFC7540"/>) on the same
host using the indicated port 8000.
</postamble>
</figure>
<figure>
<preamble>An example involving a change of host:</preamble>
<artwork type="example"><![CDATA[
Alt-Svc: h2="new.example.org:80"
]]></artwork>
<postamble>
This indicates the "h2" protocol on the host "new.example.org", running
on port 80. Note that the "quoted-string" syntax needs to be used because
":" is not an allowed character in "token".
</postamble>
</figure>
<texttable style="all" align="left">
<preamble>Examples for protocol name escaping:</preamble>
<ttcol>ALPN protocol name</ttcol>
<ttcol>protocol-id</ttcol>
<ttcol>Note</ttcol>
<c>h2</c>
<c>h2</c>
<c>No escaping needed</c>
<c>w=x:y#z</c>
<c>w%3Dx%3Ay#z</c>
<c>"=" and ":" escaped</c>
<c>x%y</c>
<c>x%25y</c>
<c>"%" needs escaping</c>
</texttable>
<t>
Alt-Svc MAY occur in any HTTP response message, regardless of the status code.
Note that recipients of Alt-Svc are free to ignore the header field (and indeed
need to in some situations; see Sections <xref format="counter" target="host_auth"/> and <xref format="counter" target="status"/>).
</t>
<figure>
<preamble>The Alt-Svc field value can have multiple values:</preamble>
<artwork type="example"><![CDATA[
Alt-Svc: h2c=":8000", h2=":443"
]]></artwork>
</figure>
<t>
When multiple values are present, the order of the values reflects the server's
preference (with the first value being the most preferred alternative).
</t>
<t>
The value(s) advertised by Alt-Svc can be used by clients to open a new
connection to an alternative service. Subsequent requests can start using this new connection
immediately, or can continue using the existing connection while the new connection is created.
</t>
<t>
When using HTTP/2 (<xref target="RFC7540"/>), servers SHOULD instead send an ALTSVC frame
(<xref target="frame"/>). A single ALTSVC frame can be sent for a connection;
a new frame is not needed for every request. Note that, despite this
recommendation, Alt-Svc header fields remain valid in responses delivered over HTTP/2.
</t>
<t>
Each "alt-value" is followed by an OPTIONAL semicolon-separated list of
additional parameters, each such "parameter" comprising a name and a value.
</t>
<t>
This specification defines two parameters: "ma" and "persist", defined in
<xref target="caching-alt-svc-header-field-values"/>. Unknown parameters
MUST be ignored, that is the values (alt-value) they appear in MUST
be processed as if the unknown parameter was not present.
</t>
<t>
New parameters can be defined in extension specifications (see
<xref target="iana.parameters"/> for registration details).
</t>
<t>
Note that all field elements that allow "quoted-string" syntax MUST be processed
as per Section 3.2.6 of <xref target="RFC7230"/>.
</t>
<section anchor="caching-alt-svc-header-field-values" title="Caching Alt-Svc Header Field Values">
<t>
When an alternative service is advertised using Alt-Svc, it is considered fresh
for 24 hours from generation of the message. This can be modified with the 'ma'
(max-age) parameter.
</t>
<figure><preamble>Syntax:</preamble><artwork type="abnf2616"><![CDATA[
ma = delta-seconds; see [RFC7234], Section 1.2.1
]]></artwork></figure>
<t>
The delta-seconds value indicates the number of seconds since the response was generated the
alternative service is considered fresh for.
</t>
<figure>
<artwork type="example"><![CDATA[
Alt-Svc: h2=":443"; ma=3600
]]></artwork>
</figure>
<t>
See Section 4.2.3 of <xref target="RFC7234"/> for details of determining
response age.
</t>
<figure>
<preamble>For example, a response:</preamble>
<artwork type="message/http; msgtype="response""><![CDATA[
HTTP/1.1 200 OK
Content-Type: text/html
Cache-Control: max-age=600
Age: 30
Alt-Svc: h2c=":8000"; ma=60
]]></artwork>
<postamble>
indicates that an alternative service is available and usable for the next 60
seconds. However, the response has already been cached for 30 seconds (as per
the Age header field value), so therefore the alternative service is only fresh
for the 30 seconds from when this response was received, minus estimated
transit time.
</postamble>
</figure>
<t>
Note that the freshness lifetime for HTTP caching (here, 600 seconds) does not
affect caching of Alt-Svc values.
</t>
<t>
When an Alt-Svc response header field is received from an origin, its value
invalidates and replaces all cached alternative services for that origin.
</t>
<t>
By default, cached alternative services will be cleared when the client detects a network
change. Alternative services that are intended to be longer-lived (e.g., those that are not
specific to the client access network) can carry the "persist" parameter with a value "1" as a
hint that the service is potentially useful beyond a network configuration change.
</t><figure>
<preamble>Syntax:</preamble>
<artwork type="abnf2616"><![CDATA[
persist = "1"
]]></artwork></figure>
<t>
For example:
</t>
<figure>
<artwork type="example"><![CDATA[
Alt-Svc: h2=":443"; ma=2592000; persist=1
]]></artwork>
</figure>
<t>
This specification only a defines a single value for "persist". Clients
MUST ignore "persist" parameters with values other than "1".
</t>
<t>
See <xref target="caching"/> for general requirements on caching alternative services.
</t>
</section>
</section>
<section anchor="frame" title="The ALTSVC HTTP/2 Frame">
<t>
The ALTSVC HTTP/2 frame (<xref target="RFC7540"/>, Section 4)
advertises the availability of an alternative service to an HTTP/2 client.
</t>
<t>
The ALTSVC frame is a non-critical extension to HTTP/2. Endpoints that do
not support this frame can safely ignore it.
</t>
<t>
An ALTSVC frame from a server to a client on a stream other than stream 0
indicates that the conveyed alternative service is associated with the origin
of that stream.
</t>
<t>
An ALTSVC frame from a server to a client on stream 0 indicates that the conveyed alternative
service is associated with the origin contained in the Origin field of the frame. An association
with an origin that the client does not consider authoritative for the current connection MUST
be ignored.
</t>
<t>
The ALTSVC frame type is 0xa (decimal 10).
</t>
<figure title="ALTSVC Frame Payload">
<artwork type="drawing"><![CDATA[
+-------------------------------+-------------------------------+
| Origin-Len (16) | Origin? (*) ...
+-------------------------------+-------------------------------+
| Alt-Svc-Field-Value (*) ...
+---------------------------------------------------------------+
]]></artwork>
</figure>
<t>
The ALTSVC frame contains the following fields:
<list style="hanging">
<t hangText="Origin-Len:">
An unsigned, 16-bit integer indicating the length, in octets, of the Origin field.
</t>
<t hangText="Origin:">
An OPTIONAL sequence of characters containing the ASCII serialization of an
origin (<xref target="RFC6454"/>, Section 6.2) that the alternative
service is applicable to.
</t>
<t hangText="Alt-Svc-Field-Value:">
A sequence of octets (length determined by subtracting the length of all preceding fields
from the frame length) containing a value identical to the Alt-Svc field value defined in
<xref target="alt-svc"/> (ABNF production "Alt-Svc").
</t>
</list>
</t>
<t>
The ALTSVC frame does not define any flags.
</t>
<t>
The ALTSVC frame is intended for receipt by clients; a server that receives an
ALTSVC frame can safely ignore it.
</t>
<t>
An ALTSVC frame on stream 0 with empty (length 0) "Origin" information is
invalid and MUST be ignored. An ALTSVC frame on a stream other than stream
0 containing non-empty "Origin" information is invalid and MUST be ignored.
</t>
<t>
The ALTSVC frame is processed hop-by-hop. An intermediary MUST NOT forward ALTSVC frames,
though it can use the information contained in ALTSVC frames in forming new ALTSVC frames
to send to its own clients.
</t>
<t>
Receiving an ALTSVC frame is semantically equivalent to receiving an Alt-Svc
header field. As a result, the ALTSVC frame causes alternative services for
the corresponding origin to be replaced. Note that it would be unwise to mix
the use of Alt-Svc header fields with the use of ALTSVC frames, as the sequence
of receipt might be hard to predict.
</t>
</section>
<section anchor="indicator" title="The Alt-Used HTTP Header Field">
<t>
The Alt-Used header field is used in requests to indicate the identity of
the alternative service in use, just as the Host header field (Section 5.4 of <xref target="RFC7230"/>)
identifies the host and port of the origin.
</t>
<figure>
<artwork type="abnf2616"><![CDATA[
Alt-Used = uri-host [ ":" port ]
]]></artwork>
</figure>
<t>
Alt-Used is intended to allow alternative services to detect loops, differentiate
traffic for purposes of load balancing, and generally to ensure that it is
possible to identify the intended destination of traffic, since introducing
this information after a protocol is in use has proven to be problematic.
</t>
<t>
When using an alternative service, clients SHOULD include an Alt-Used
header field in all requests.
</t>
<figure>
<preamble>For example:</preamble>
<artwork type="message/http; msgtype="request""><![CDATA[
GET /thing HTTP/1.1
Host: origin.example.com
Alt-Used: alternate.example.net
]]></artwork>
</figure>
</section>
<section anchor="status" title="The 421 Misdirected Request HTTP Status Code">
<t>
The 421 (Misdirected Request) status code is defined in Section 9.1.2 of <xref target="RFC7540"/> to indicate that the current server
instance is not authoritative for the requested resource. This can be used
to indicate that an alternative service is not authoritative; see <xref target="alternative"/>).
</t>
<t>
Clients receiving 421 (Misdirected Request) from an alternative service MUST
remove the corresponding entry from its alternative service cache (see <xref target="caching"/>) for that origin. Regardless of the idempotency of the
request method, they MAY retry the request, either at another alternative
server, or at the origin.
</t>
<t>
An Alt-Svc header field in a 421 (Misdirected Request) response MUST be ignored.
</t>
</section>
<section anchor="iana-considerations" title="IANA Considerations">
<section title="Header Field Registrations">
<t>
HTTP header fields are registered within the "Message Headers" registry
maintained at
<eref target="https://www.iana.org/assignments/message-headers/"/>.
</t>
<t>
This document defines the following HTTP header fields, so their associated
registry entries shall be added according to the permanent registrations below
(see <xref target="BCP90"/>):
</t>
<texttable align="left" suppress-title="true" anchor="iana.header.registration.table">
<ttcol>Header Field Name</ttcol>
<ttcol>Protocol</ttcol>
<ttcol>Status</ttcol>
<ttcol>Reference</ttcol>
<c>Alt-Svc</c>
<c>http</c>
<c>standard</c>
<c>
<xref target="alt-svc"/>
</c>
<c>Alt-Used</c>
<c>http</c>
<c>standard</c>
<c>
<xref target="indicator"/>
</c>
</texttable>
<t>
The change controller is: "IETF (iesg@ietf.org) - Internet Engineering Task Force".
</t>
</section>
<section anchor="alt-svc-frame-registration" title="The ALTSVC HTTP/2 Frame Type">
<t>
This document registers the ALTSVC frame type in the HTTP/2 Frame Types
registry (<xref target="RFC7540"/>, Section 11.2).
<list style="empty">
<t>Frame Type: ALTSVC</t>
<t>Code: 0xa</t>
<t>Specification: <xref target="frame"/> of this document</t>
</list>
</t>
</section>
<section anchor="iana.parameters" title="Alt-Svc Parameter Registry">
<t>
The HTTP Alt-Svc Parameter Registry defines the name space for
parameters. It will be created and maintained at (the suggested URI)
<eref target="http://www.iana.org/assignments/http-alt-svc-parameters"/>.
</t>
<section anchor="parameter.registry.procedure" title="Procedure">
<t>
A registration MUST include the following fields:
<list style="symbols">
<t>Parameter Name</t>
<t>Pointer to specification text</t>
</list>
</t>
<t>
Values to be added to this name space require Expert Review (see <xref target="RFC5226"/>, Section 4.1).
</t>
</section>
<section anchor="parameter.registrations" title="Registrations">
<t>
The HTTP Alt-Svc Parameter Registry is to be populated with the registrations below:
</t>
<texttable align="left" suppress-title="true">
<ttcol>Alt-Svc Parameter</ttcol>
<ttcol>Reference</ttcol>
<c>ma</c>
<c>
<xref target="caching-alt-svc-header-field-values"/>
</c>
<c>persist</c>
<c>
<xref target="caching-alt-svc-header-field-values"/>
</c>
</texttable>
</section>
</section>
</section>
<section anchor="internationalization-considerations" title="Internationalization Considerations">
<t>
An internationalized domain name that appears in either the header field
(<xref target="alt-svc"/>) or the HTTP/2 frame (<xref target="frame"/>)
MUST be expressed using A-labels (<xref target="RFC5890"/>, Section 2.3.2.1).
</t>
</section>
<section anchor="security-considerations" title="Security Considerations">
<section anchor="changing-ports" title="Changing Ports">
<t>
Using an alternative service implies accessing an origin's resources on an
alternative port, at a minimum. An attacker that can inject alternative services
and listen at the advertised port is therefore able to hijack an origin. On
certain servers, it is normal for users to be able to control some personal
pages available on a shared port, and also to accept to requests on less-privileged
ports.
</t>
<t>
For example, an attacker that can add HTTP response header fields to some pages
can redirect traffic for an entire origin to a different port on the same host
using the Alt-Svc header field; if that port is under the attacker's control,
they can thus masquerade as the HTTP server.
</t>
<t>
On servers, this risk can be reduced by restricting the ability to advertise
alternative services, and restricting who can open a port for listening on that host.
Clients can reduce this risk by imposing stronger requirements (e.g. strong
authentication) when moving from System Ports to User or Dynamic Ports, or from
User Ports to Dynamic Ports, as defined in Section 6 of <xref target="RFC6335"/>.
</t>
<t>
It is always valid for a client to ignore an alternative service advertisement which
does not meet its implementation-specific security requirements. Servers can increase
the likelihood of clients using the alternative service by providing strong
authentication even when not required.
</t>
</section>
<section anchor="host_security" title="Changing Hosts">
<t>
When the host is changed due to the use of an alternative service, it presents
an opportunity for attackers to hijack communication to an origin.
</t>
<t>
For example, if an attacker can convince a user agent to send all traffic for
"innocent.example.org" to "evil.example.com" by successfully associating it as an alternative
service, they can masquerade as that origin. This can be done locally (see mitigations in <xref target="changing-ports"/>) or remotely (e.g., by an intermediary as a man-in-the-middle attack).
</t>
<t>
This is the reason for the requirement in <xref target="host_auth"/> that any alternative
service with a host different from the origin's be strongly authenticated with
the origin's identity; i.e., presenting a certificate for the origin proves
that the alternative service is authorized to serve traffic for the origin.
</t>
<t>
However, this authorization is only as strong as the method used to
authenticate the alternative service. In particular, there are well-known
exploits to make an attacker's certificate appear as legitimate.
</t>
<t>
Alternative services could be used to persist such an attack; for example, an
intermediary could man-in-the-middle TLS-protected communication to a target,
and then direct all traffic to an alternative service with a large freshness
lifetime, so that the user agent still directs traffic to the attacker even when
not using the intermediary.
</t>
<t>
Implementations MUST perform any certificate-pinning validation (e.g.
<xref target="RFC7469"/>) on alternative services just as they would on direct
connections to the origin. Implementations might also choose to add
other requirements around which certificates are acceptable for alternative
services.
</t>
</section>
<section anchor="changing-protocols" title="Changing Protocols">
<t>
When the ALPN protocol is changed due to the use of an alternative service, the
security properties of the new connection to the origin can be different from
that of the "normal" connection to the origin, because the protocol identifier
itself implies this.
</t>
<t>
For example, if an "https://" URI has a protocol advertised that does not use
some form of end-to-end encryption (most likely, TLS), it violates the
expectations for security that the URI scheme implies.
</t>
<t>
Therefore, clients cannot blindly use alternative services, but instead evaluate
the option(s) presented to assure that security requirements and expectations
(of specifications, implementations and end users) are met.
</t>
</section>
<section anchor="tracking" title="Tracking Clients Using Alternative Services">
<t>
Choosing an alternative service implies connecting to a new, server-supplied
host name. By using many different (potentially unique) host names, servers
could conceivably track client requests. Such tracking could follow users
across multiple networks, when the "persist" flag is used.
</t>
<t>
Clients that wish to prevent requests from being correlated (such as those
that offer modes aimed at providing improved privacy) can decide not to use
alternative services for multiple requests that would not otherwise be
allowed to be correlated.
</t>
<t>
In a user agent, any alternative service information MUST be removed when origin-specific data
is cleared (for instance, when cookies are cleared).
</t>
</section>
<section anchor="confusion-regarding-request-scheme" title="Confusion Regarding Request Scheme">
<t>
Some server-side HTTP applications make assumptions about security based upon
connection context; for example, equating being served upon port 443 with the
use of an "https://" URI (and the various security properties that implies).
</t>
<t>
This affects not only the security properties of the connection itself, but
also the state of the client at the other end of it; for example, a Web
browser treats "https://" URIs differently than "http://" URIs in many ways, not just
for purposes of protocol handling.
</t>
<t>
Since one of the uses of Alternative Services is to allow a connection to be
migrated to a different protocol and port, these applications can become
confused about the security properties of a given connection, sending
information (e.g., cookies, content) that is intended for a secure context
(e.g., an "https://" URI) to a client that is not treating it as one.
</t>
<t>
This risk can be mitigated in servers by using the URI scheme explicitly
carried by the protocol (e.g., ":scheme" in HTTP/2 or the "absolute form" of
the request target in HTTP/1.1) as an indication of security context, instead of
other connection properties (<xref target="RFC7540"/>, Section 8.1.2.3
and <xref target="RFC7230"/>, Section 5.3.2).
</t>
<t>
When the protocol does not explicitly carry the scheme (e.g., as is usually
the case for HTTP/1.1 over TLS, servers can mitigate this risk by either
assuming that all requests have an insecure context, or by refraining from
advertising alternative services for insecure schemes (such as HTTP).
</t>
</section>
</section>
</middle>
<back>
<references title="Normative References">
<reference anchor="RFC2119" target="http://www.rfc-editor.org/info/rfc2119"><front>
<title abbrev="RFC Key Words">Key words for use in RFCs to Indicate Requirement Levels</title>
<author initials="S." surname="Bradner" fullname="Scott Bradner">
<organization>Harvard University</organization>
</author>
<date year="1997" month="March"/>
</front><seriesInfo name="BCP" value="14"/><seriesInfo name="RFC" value="2119"/><seriesInfo name="DOI" value="10.17487/RFC2119"/></reference>
<reference anchor="RFC3986" target="http://www.rfc-editor.org/info/rfc3986"><front>
<title abbrev="URI Generic Syntax">Uniform Resource Identifier (URI): Generic Syntax</title>
<author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
<organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
</author>
<author initials="R." surname="Fielding" fullname="Roy T. Fielding">
<organization abbrev="Day Software">Day Software</organization>
</author>
<author initials="L." surname="Masinter" fullname="Larry Masinter">
<organization abbrev="Adobe Systems">Adobe Systems Incorporated</organization>
</author>
<date year="2005" month="January"/>
</front><seriesInfo name="STD" value="66"/><seriesInfo name="RFC" value="3986"/><seriesInfo name="DOI" value="10.17487/RFC3986"/></reference>
<reference anchor="RFC5226" target="http://www.rfc-editor.org/info/rfc5226"><front>
<title>Guidelines for Writing an IANA Considerations Section in RFCs</title>
<author initials="T." surname="Narten" fullname="T. Narten"/>
<author initials="H." surname="Alvestrand" fullname="H. Alvestrand"/>
<date year="2008" month="May"/>
</front><seriesInfo name="BCP" value="26"/><seriesInfo name="RFC" value="5226"/><seriesInfo name="DOI" value="10.17487/RFC5226"/></reference>
<reference anchor="RFC5234" target="http://www.rfc-editor.org/info/rfc5234"><front>
<title>Augmented BNF for Syntax Specifications: ABNF</title>
<author initials="D." surname="Crocker" fullname="D. Crocker" role="editor"/>
<author initials="P." surname="Overell" fullname="P. Overell"/>
<date year="2008" month="January"/>
</front><seriesInfo name="STD" value="68"/><seriesInfo name="RFC" value="5234"/><seriesInfo name="DOI" value="10.17487/RFC5234"/></reference>
<reference anchor="RFC5890" target="http://www.rfc-editor.org/info/rfc5890"><front>
<title>
Internationalized Domain Names for Applications (IDNA): Definitions and
Document Framework
</title>
<author initials="J." surname="Klensin" fullname="John Klensin"/>
<date year="2010" month="August"/>
</front><seriesInfo name="RFC" value="5890"/><seriesInfo name="DOI" value="10.17487/RFC5890"/></reference>
<reference anchor="RFC6066" target="http://www.rfc-editor.org/info/rfc6066"><front>
<title>Transport Layer Security (TLS) Extensions: Extension Definitions</title>
<author initials="D." surname="Eastlake" fullname="D. Eastlake"/>
<date year="2011" month="January"/>
</front><seriesInfo name="RFC" value="6066"/><seriesInfo name="DOI" value="10.17487/RFC6066"/></reference>
<reference anchor="RFC6454" target="http://www.rfc-editor.org/info/rfc6454"><front>
<title>The Web Origin Concept</title>
<author initials="A." surname="Barth" fullname="A. Barth"/>
<date year="2011" month="December"/>
</front><seriesInfo name="RFC" value="6454"/><seriesInfo name="DOI" value="10.17487/RFC6454"/></reference>
<reference anchor="RFC7230" target="http://www.rfc-editor.org/info/rfc7230"><front>
<title>Hypertext Transfer Protocol (HTTP/1.1): Message Syntax and Routing</title>
<author fullname="Roy T. Fielding" initials="R." role="editor" surname="Fielding">
<organization abbrev="Adobe">Adobe Systems Incorporated</organization>
<address><email>fielding@gbiv.com</email></address>
</author>
<author fullname="Julian F. Reschke" initials="J. F." role="editor" surname="Reschke">
<organization abbrev="greenbytes">greenbytes GmbH</organization>
<address><email>julian.reschke@greenbytes.de</email></address>
</author>
<date month="June" year="2014"/>
</front><seriesInfo name="RFC" value="7230"/><seriesInfo name="DOI" value="10.17487/RFC7230"/></reference>
<reference anchor="RFC7234" target="http://www.rfc-editor.org/info/rfc7234"><front>
<title>Hypertext Transfer Protocol (HTTP/1.1): Caching</title>
<author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
<organization abbrev="Adobe">Adobe Systems Incorporated</organization>
<address><email>fielding@gbiv.com</email></address>
</author>
<author fullname="Mark Nottingham" initials="M." role="editor" surname="Nottingham">
<organization>Akamai</organization>
<address><email>mnot@mnot.net</email></address>
</author>
<author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
<organization abbrev="greenbytes">greenbytes GmbH</organization>
<address><email>julian.reschke@greenbytes.de</email></address>
</author>
<date month="June" year="2014"/>
</front><seriesInfo name="RFC" value="7234"/><seriesInfo name="DOI" value="10.17487/RFC7234"/></reference>
<reference anchor="RFC7301" target="http://www.rfc-editor.org/info/rfc7301"><front>
<title>Transport Layer Security (TLS) Application-Layer Protocol Negotiation Extension</title>
<author initials="S." surname="Friedl" fullname="Stephan Friedl"/>
<author initials="A." surname="Popov" fullname="Andrey Popov"/>
<author initials="A." surname="Langley" fullname="Adam Langley"/>
<author initials="S." surname="Emile" fullname="Stephan Emile"/>
<date month="July" year="2014"/>
</front><seriesInfo name="RFC" value="7301"/><seriesInfo name="DOI" value="10.17487/RFC7301"/></reference>
<reference anchor="RFC7405" target="http://www.rfc-editor.org/info/rfc7405"><front>
<title>Case-Sensitive String Support in ABNF</title>
<author initials="P." surname="Kyzivat" fullname="Paul Kyzivat"/>
<date year="2014" month="December"/>
</front><seriesInfo name="RFC" value="7405"/><seriesInfo name="DOI" value="10.17487/RFC7405"/></reference>
<reference anchor="RFC7540" target="http://www.rfc-editor.org/info/rfc7540"><front>
<title>Hypertext Transfer Protocol version 2</title>
<author initials="M." surname="Belshe" fullname="Mike Belshe"/>
<author initials="R." surname="Peon" fullname="Roberto Peon"/>
<author initials="M." surname="Thomson" fullname="Martin Thomson" role="editor"/>
<date month="May" year="2015"/>
</front><seriesInfo name="RFC" value="7540"/><seriesInfo name="DOI" value="10.17487/RFC7540"/></reference>
</references>
<references title="Informative References">
<reference anchor="BCP90" target="http://www.rfc-editor.org/info/bcp90"><front>
<title>Registration Procedures for Message Header Fields</title>
<author initials="G." surname="Klyne" fullname="G. Klyne"/>
<author initials="M." surname="Nottingham" fullname="M. Nottingham"/>
<author initials="J." surname="Mogul" fullname="J. Mogul"/>
<date year="2004" month="September"/>
</front><seriesInfo name="BCP" value="90"/><seriesInfo name="RFC" value="3864"/></reference>
<reference anchor="RFC5246" target="http://www.rfc-editor.org/info/rfc5246"><front>
<title>The Transport Layer Security (TLS) Protocol Version 1.2</title>
<author initials="T." surname="Dierks" fullname="T. Dierks"/>
<author initials="E." surname="Rescorla" fullname="E. Rescorla"/>
<date year="2008" month="August"/>
</front><seriesInfo name="RFC" value="5246"/><seriesInfo name="DOI" value="10.17487/RFC5246"/></reference>
<reference anchor="RFC6335" target="http://www.rfc-editor.org/info/rfc6335"><front>
<title>Internet Assigned Numbers Authority (IANA) Procedures for the Management
of the Service Name and Transport Protocol Port Number Registry</title>
<author initials="M." surname="Cotton" fullname="M. Cotton"/>
<author initials="L." surname="Eggert" fullname="L. Eggert"/>
<author initials="J." surname="Touch" fullname="J. Touch"/>
<author initials="M." surname="Westerlund" fullname="M. Westerlund"/>
<author initials="S." surname="Cheshire" fullname="S. Cheshire"/>
<date year="2011" month="August"/>
</front><seriesInfo name="RFC" value="6335"/><seriesInfo name="DOI" value="10.17487/RFC6335"/></reference>
<reference anchor="RFC7469" target="http://www.rfc-editor.org/info/rfc7469"><front>
<title>Public Key Pinning Extension for HTTP</title>
<author initials="C." surname="Evans" fullname="Chris Evans"/>
<author initials="C." surname="Palmer" fullname="Chris Palmer"/>
<author initials="R." surname="Sleevi" fullname="Ryan Sleevi"/>
<date month="April" year="2015"/>
</front><seriesInfo name="RFC" value="7469"/><seriesInfo name="DOI" value="10.17487/RFC7469"/></reference>
</references>
<section anchor="change.log" title="Change Log (to be removed by RFC Editor before publication)">
<section anchor="changes.since.draft-nottingham-httpbis-alt-svc-05" title="Since draft-nottingham-httpbis-alt-svc-05">
<t>
This is the first version after adoption of draft-nottingham-httpbis-alt-svc-05
as Working Group work item. It only contains editorial changes.
</t>
</section>
<section anchor="changes.since.draft-ietf-httpbis-alt-svc-00" title="Since draft-ietf-httpbis-alt-svc-00">
<t>
Selected 421 as proposed status code for "Not Authoritative".
</t>
<t>
Changed header field syntax to use percent-encoding of ALPN protocol names
(<eref target="https://github.com/http2/http2-spec/issues/446"/>).
</t>
</section>
<section anchor="changes.since.draft-ietf-httpbis-alt-svc-01" title="Since draft-ietf-httpbis-alt-svc-01">
<t>
Updated HTTP/1.1 references.
</t>
<t>
Renamed "Service" to "Alt-Svc-Used" and reduced information to a flag to address
fingerprinting concerns (<eref target="https://github.com/http2/http2-spec/issues/502"/>).
</t>
<t>
Note that ALTSVC frame is preferred to Alt-Svc header field (<eref target="https://github.com/http2/http2-spec/pull/503"/>).
</t>
<t>
Incorporate ALTSRV frame (<eref target="https://github.com/http2/http2-spec/pull/507"/>).
</t>
<t>
Moved definition of status code 421 to HTTP/2.
</t>
<t>
Partly resolved <eref target="https://github.com/httpwg/http-extensions/issues/5"/>.
</t>
</section>
<section anchor="changes.since.draft-ietf-httpbis-alt-svc-02" title="Since draft-ietf-httpbis-alt-svc-02">
<t>
Updated ALPN reference.
</t>
<t>
Resolved <eref target="https://github.com/httpwg/http-extensions/issues/2"/>.
</t>
</section>
<section anchor="changes.since.draft-ietf-httpbis-alt-svc-03" title="Since draft-ietf-httpbis-alt-svc-03">
<t>
Renamed "Alt-Svc-Used" to "Alt-Used" (<eref target="https://github.com/httpwg/http-extensions/issues/17"/>).
</t>
<t>
Clarify ALTSVC Origin information requirements (<eref target="https://github.com/httpwg/http-extensions/issues/19"/>).
</t>
<t>
Remove/tune language with respect to tracking risks (see <eref target="https://github.com/httpwg/http-extensions/issues/34"/>).
</t>
</section>
<section anchor="changes.since.draft-ietf-httpbis-alt-svc-04" title="Since draft-ietf-httpbis-alt-svc-04">
<t>
Mention tracking by alt-svc host name in Security Considerations (<eref target="https://github.com/httpwg/http-extensions/issues/36"/>).
</t>
<t>
"421 (Not Authoritative)" -> "421 (Misdirected Request)".
</t>
<t>
Allow the frame to carry multiple indicator and use the same payload formats for both
(<eref target="https://github.com/httpwg/http-extensions/issues/37"/>).
</t>
</section>
<section anchor="changes.since.draft-ietf-httpbis-alt-svc-05" title="Since draft-ietf-httpbis-alt-svc-05">
<t>
Go back to specifying the origin in Alt-Used, but make it a "SHOULD"
(<eref target="https://github.com/httpwg/http-extensions/issues/34"/>).
</t>
<t>
Restore Origin field in ALT-SVC frame
(<eref target="https://github.com/httpwg/http-extensions/issues/38"/>).
</t>
</section>
<section anchor="changes.since.draft-ietf-httpbis-alt-svc-06" title="Since draft-ietf-httpbis-alt-svc-06">
<t>
Disallow use of alternative services when the protocol might not carry
the scheme
(<eref target="https://github.com/httpwg/http-extensions/issues/12"/>).
</t>
<t>
Align opp-sec and alt-svc
(<eref target="https://github.com/httpwg/http-extensions/issues/33"/>).
</t>
<t>
alt svc frame on pushed (even and non-0) frame
(<eref target="https://github.com/httpwg/http-extensions/issues/44"/>).
</t>
<t>
"browser" -> "user agent"
(<eref target="https://github.com/httpwg/http-extensions/pull/61"/>).
</t>
<t>
ABNF for "parameter"
(<eref target="https://github.com/httpwg/http-extensions/issues/65"/>).
</t>
<t>
Updated HTTP/2 reference.
</t>
</section>
<section anchor="changes.since.draft-ietf-httpbis-alt-svc-07" title="Since draft-ietf-httpbis-alt-svc-07">
<t>
Alt-Svc alternative cache invalidation
(<eref target="https://github.com/httpwg/http-extensions/issues/16"/>).
</t>
<t>
Unexpected Alt-Svc frames
(<eref target="https://github.com/httpwg/http-extensions/issues/18"/>).
</t>
<t>
Associating Alt-Svc header with an origin
(<eref target="https://github.com/httpwg/http-extensions/issues/21"/>).
</t>
<t>
ALPN identifiers in Alt-Svc
(<eref target="https://github.com/httpwg/http-extensions/issues/43"/>).
</t>
<t>
Number of alternate services used
(<eref target="https://github.com/httpwg/http-extensions/issues/58"/>).
</t>
<t>
Proxy and .pac interaction
(<eref target="https://github.com/httpwg/http-extensions/issues/62"/>).
</t>
<t>
Need to define extensibility for alt-svc parameters
(<eref target="https://github.com/httpwg/http-extensions/issues/69"/>).
</t>
<t>
Persistence of alternates across network changes
(<eref target="https://github.com/httpwg/http-extensions/issues/71"/>).
</t>
<t>
Alt-Svc header with 421 status
(<eref target="https://github.com/httpwg/http-extensions/issues/75"/>).
</t>
<t>
Incorporate several editorial improvements suggested by Mike Bishop
(<eref target="https://github.com/httpwg/http-extensions/pull/77"/>,
<eref target="https://github.com/httpwg/http-extensions/pull/78"/>).
</t>
<t>
Alt-Svc response header field in HTTP/2 frame
(<eref target="https://github.com/httpwg/http-extensions/issues/87"/>).
</t>
</section>
<section anchor="changes.since.draft-ietf-httpbis-alt-svc-08" title="Since draft-ietf-httpbis-alt-svc-08">
<t>
Remove left over text about ext-params, applying to an earlier version
of Alt-Used
(see <eref target="https://github.com/httpwg/http-extensions/issues/34"/>).
</t>
<t>
Conflicts between Alt-Svc and ALPN
(<eref target="https://github.com/httpwg/http-extensions/issues/72"/>).
</t>
<t>
Elevation of privilege
(<eref target="https://github.com/httpwg/http-extensions/issues/73"/>).
</t>
<t>
Alternates of alternates
(<eref target="https://github.com/httpwg/http-extensions/issues/74"/>).
</t>
<t>
Alt-Svc and Cert Pinning
(<eref target="https://github.com/httpwg/http-extensions/issues/76"/>).
</t>
<t>
Using alt-svc on localhost
(no change to spec, see <eref target="https://github.com/httpwg/http-extensions/issues/89"/>).
</t>
<t>
IANA procedure for alt-svc parameters
(<eref target="https://github.com/httpwg/http-extensions/issues/96"/>).
</t>
<t>
Alt-svc from https (1.1) to https (1.1)
(<eref target="https://github.com/httpwg/http-extensions/issues/91"/>).
</t>
<t>
Alt-svc vs the ability to convey the scheme inside the protocol
(<eref target="https://github.com/httpwg/http-extensions/issues/92"/>).
</t>
<t>
Reconciling MAY/can vs. SHOULD
(<eref target="https://github.com/httpwg/http-extensions/issues/101"/>).
</t>
<t>
Typo in alt-svc caching example
(<eref target="https://github.com/httpwg/http-extensions/issues/117"/>).
</t>
</section>
<section anchor="changes.since.draft-ietf-httpbis-alt-svc-09" title="Since draft-ietf-httpbis-alt-svc-09">
<t>
Editorial improvements
(<eref target="https://github.com/httpwg/http-extensions/issues/118"/>,
<eref target="https://github.com/httpwg/http-extensions/issues/119"/>,
<eref target="https://github.com/httpwg/http-extensions/issues/120"/>,
<eref target="https://github.com/httpwg/http-extensions/issues/121"/>,
<eref target="https://github.com/httpwg/http-extensions/issues/122"/>,
<eref target="https://github.com/httpwg/http-extensions/issues/123"/>,
<eref target="https://github.com/httpwg/http-extensions/issues/125"/>,
<eref target="https://github.com/httpwg/http-extensions/issues/126"/>).
</t>
</section>
<section anchor="changes.since.draft-ietf-httpbis-alt-svc-10" title="Since draft-ietf-httpbis-alt-svc-10">
<t>
Editorial improvements
(<eref target="https://github.com/httpwg/http-extensions/issues/130"/>).
</t>
<t>
Use RFC 7405 ABNF extension
(<eref target="https://github.com/httpwg/http-extensions/issues/131"/>).
</t>
</section>
</section>
<section anchor="acknowledgements" title="Acknowledgements">
<t>
Thanks to Adam Langley, Bence Beky, Eliot Lear, Erik Nygren, Guy Podjarny,
Herve Ruellan, Lucas Pardue, Martin Thomson, Matthew Kerwin, Mike Bishop,
Paul Hoffman,
Richard Barnes, Richard Bradbury, Stephen Farrell, Stephen Ludin,
and Will Chan for their
feedback and suggestions.
</t>
<t>
The Alt-Svc header field was influenced by the design of the
Alternate-Protocol header field in SPDY.
</t>
</section>
</back>
</rfc>| PAFTECH AB 2003-2026 | 2026-04-24 04:24:26 |